1. Field of the Invention
The present invention relates to a duplex printer, which repeatedly prints a pattern on an information non-printing side of a printing medium, when printing information consisting of image and character on an information printing side of a printing medium.
2. Description of the Related Art
Generally, a printer prints information consisting of image and characters on a printing medium. When printing information, a printing head of a printer is faced to a front side (information printing side) as a first side of a printing medium. A printer feeds a printing medium, and prints information on it in this state. Therefore, information is printed only on a front side of a printing medium. Nothing is printed on a back side (information non-printing side) as a second side of a printing medium. When a receipt or ticket is issued, a fixed pattern or advertisement is already printed on a back side of a receipt or ticket. A printing medium with a fixed pattern or advertisement preprinted on a back side is used for a receipt or ticket.
For example, U.S. Pat. No. 6,759,366 discloses a duplex printer having two thermal heads. This duplex printer prints both sides of a printing medium (heat-sensitive paper). The duplex printer has two platens. A first thermal head and a first platen are arranged opposite to each other. A second thermal head and a second platen are arranged opposite to each other. A printing medium is held and conveyed by these thermal heads and platens. The first thermal head and first platen are arranged in the upstream of the second thermal head and second platen in the conveying direction. Therefore, the duplex printer prints information on both sides of a printing medium substantially at the same time.
When information is printed only on the front side of a printing medium, information not to be printed on the front side (hereinafter called a first information) is successively printed on the front side of a printing medium of size different from the printing medium whose front side has been printed, or on the front side of the printing medium whose front side has been printed. As a result, if first information is printed on the front side of a printing medium of the size different from the printing medium whose front side has been printed, the number of kinds of printing medium to be managed in increased. This increases the number of needless printing medium stock. When first information is successively printed on a front side of a printing medium that is already printed, the amount of using a printing medium is increased.
In a printing medium whose back side has been printed, information different from information printed on the front side has been printed on the back side. Thus, the amount of using a printing medium when printing the front side and back side, is smaller than the amount of using a printing medium when printing only the front side. However, as a different printer is used for printing, a printing medium whose back side is already printed requires a relatively high cost. If advertisement or notice information is already printed on a printing medium used as a roll paper such as a receipt and ticket, the printed information goes out of date as the printing medium is used for a long time. For example, a printing medium with printed advertisement is prepared assuming the amount of use before the advertisement period, and will be unusable after the effective advertisement period is expired, and the printing medium will be discarded. As for a fixed pattern, it has been printed, and cannot be easily changed by the user.